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Psychedex
Facts label

Mephenaqualone Facts

Depressant; Sedative; Quinazolinone; GABA-A receptor positive allosteric modulator

Dose and durationby route · individual sensitivity varies

Oral(mg)
Threshold< 0.5 mgLight0.5 – 1.5 mgCommon1.5 – 2.5 mgStrong2.5 – 4 mgHeavy4+ mg

Starts in 30 – 40 minLasts 15 – 20 hoursAfter-effects 6 – 12 hours

Body and dependence

Acute toxicity
Moderate
Chronic toxicity
Moderate
Physical dependence
High
Psychological dependence
High
Withdrawal
Not assessed
Compulsive redosing
Not assessed

Tolerance

Builds
Within a few days of repeated administration
Fully resets after
Not recorded
Carries over to
GABA|gabaergic; depressants

Effectslikely at a common dose

Perception
none likely · 1 possible, including Visual acuity suppression
Body
none likely · 4 possible, including Motor control impairment

Who shouldn't take it

None recorded. Not listed never means safe to take.

Combinations60 recorded

Lethal (1)
Opioids
Dangerous (21)
Alpha-2 adrenergic receptor antagonist; Antipsychotics; Atypical antipsychotics; Benzodiazepines; Buprenorphine, Kratom; Cannabis, THC; Clonidine, Guanfacine; Gabapentin, Pregabalin; GHB, Baclofen; GHB, GBL; Local anesthetics; Naltrexone; SNRIs; Stimulants; Synthetic cannabinoids; Ibogaine; Ketamine, DXM, PCP; MAOIs; NSAIDs; Poppers (Alkyl nitrites); Poppers, Nitrates
Caution (26)
See full page: psychedex.org/substances/mephenaqualone
Not graded (12)
Not listed never means safe.

Seek help immediately if

  • Extreme drowsiness — can't stay awake or be roused
  • Confusion, slurred speech, severe loss of coordination
  • Slow, shallow, or irregular breathing
  • Unconsciousness / unresponsive; limp, floppy body
  • Blue lips or fingertips
  • Vomiting while sedated (choking / aspiration risk)
  • Cold, clammy skin; weak pulse

What to do

  1. Try to wake them — shout, firm sternal rub
  2. If unresponsive or breathing is impaired, call emergency services
  3. Place them in the recovery position — critical, they can choke on vomit
  4. Monitor breathing continuously; be ready to give rescue breaths / CPR
  5. Never leave them alone to "sleep it off"
  6. Do not give other drugs, stimulants, or more depressants

Most depressant overdoses resolve with airway protection, breathing support, and monitoring. The danger is respiratory depression and choking on vomit — sharply worse when combined with opioids or alcohol. GHB/GBL overdoses often involve sudden deep unconsciousness and may self-resolve, but airway protection is essential.

988 Suicide & Crisis LifelineFireside Project: 62-FIRESIDE

psychedex.org/substances/mephenaqualone · Version r1 · Not medical adviceValues as of
On the printout